1. Field of the Invention
The present invention is directed to a reception device for detecting an electromagnetic radio-frequency wave emitted by the examination subject of a nuclear magnetic resonance tomography installation, of the type having a first reception coil, a first amplifier allocated to the first reception coil, a second reception coil whose reception signal is phase-shifted with respect to the reception signal of the first reception coil, particularly by a phase angle of 90°, comprising a second amplifier allocated to the second reception coil, and a common signal line via which the output signals of the two amplifiers are carried off.
2. Description of the Prior Art
For receiving the circularly polarized radio-frequency signal, two orthogonal polarization components are separately received in a magnetic resonance tomography installation. In, for example, a vertical field apparatus, a first polarization component is received parallel to the patient axis and a second polarization component is received perpendicular to the patient axis. For receiving the first polarization component parallel to the patient axis, a loop coil can be used that surrounds the entire patient body or an extremity to be examined. For the reception of the second polarization component, for example, a butterfly coil or saddle coil is used. Both field components of the circularly polarized magnetic field part of the electromagnetic radio-frequency signal can be detected with the separately existing reception coils or reception antennas.
The reception signals of the separately existing reception antennas are amplified in separate pre-amplifiers allocated to the reception antennas and are supplied via a 90° coupler (90° combiner) that takes the phase shift between the two polarization components into consideration to a common signal line. Via the common signal line, the radio-frequency signals combined in this way are supplied to the image evaluation, image reconstruction and image display. The phase shift between the two polarization components typically amounts to 90°. However, dependent on the structure of the magnetic resonance tomography installation, other values below this and above this are possible.
The combiner is composed of a capacitive impedance and of an inductive impedance. The output impedance of the combiner must be matched to the impedance of the common signal line. The lines leading to the combiner as well as the combiner itself must be shielded in an involved way. The known combiner also has the disadvantage that it requires a certain spatial volume for the circuitry, leading to unergonomically bulky arrangements, particularly in the manufacture of non-stationary, i.e. portable coil arrangements, for example in the manufacture of surface coils, because the combiner must be accommodated on the coil arrangement.